Eisler Liván Hernández Carrera (Spanish pronunciation: ; born February 20, 1975, in Villa Clara, Cuba) is a starting pitcher in Major League Baseball, who is currently pitching for the Washington Nationals. He is the half-brother of pitcher Orlando "El Duque" Hernández.

Hernández defected to the United States from Cuba in 1995, and has played with the Florida Marlins (1996-1999), San Francisco Giants (1999-2002), Montreal Expos (2003–2004) the Washington Nationals (formerly Montreal Expos) (2005-2006), the Arizona Diamondbacks (2006-2007), the Minnesota Twins, the Colorado Rockies (2008), and the New York Mets (2009). He bats and throws right-handed, and is known for often throwing a "slow hook," sometimes going even below 60 miles per hour, as a strikeout pitch.

A two-time All-Star, Hernández is considered to be a great defensive pitcher, having made just 11 errors in his career. He is described as a workhorse; he throws many pitches, pitches many innings, and makes every start he needs to in order to provide his team's bullpen much rest. Between 1998 and 2007, he never pitched fewer than 199 innings in any given season (in 1999 he threw "only" 199 2/3 innings). He led the National League in innings pitched in three consecutive seasons, 2003 through 2005, and led the league in complete games for the first two of those years. In 2005, he once threw 150 pitches in nine innings, although the game went into extra innings after he left. In 2004 and 2005, he led the major leagues with 3,927 and 4,009 pitches, respectively. Hernández also is a dangerous hitter, helping his own cause with the bat, and won the Silver Slugger award at the pitcher position in 2004.